Catalytic cracking of coke producing hydrocarbons

ABSTRACT

A process for thermally and catalytically upgrading a heavy feed in a single riser reactor FCC unit is disclosed. A heavy feed is added to a blast zone in the base of the riser, and sufficient hot regenerated FCC catalyst is added to induce both thermal and catalytic cracking of the heavy feed. A reactive quench material, which cools the material discharged from the blast zone is added to a quench zone downstream of the blast zone, to reduce temperature at least in part by undergoing endothermic reactions in the riser. Quench liquids can be distillable FCC feeds such as gas oil, slack wax, or alcohols or ethers. The quench material is added in an amount equal to 100 to 1000 wt % of the non-distillable material in the heavy feed. A preferred catalyst, with a high zeolite content, is used which retains activity in the quench despite initial contact with the heavy feed, which tends to overwhelm conventional FCC catalysts.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of our prior co-pendingapplication Ser. No. 165,869, filed on Mar. 3, 1988, and now abandoned,which is relied upon and incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to methods of cracking hydrocarbon feedstocks inthe presence of a cracking catalyst. More particularly, the inventionrelates to the fluid catalytic cracking of plural hydrocarbon feedstockshaving diverse cracking characteristics.

A number of processes for the cracking of hydrocarbon feedstocks viacontact at appropriate temperatures and pressures with fluidizedcatalytic particles are known in the art. These processes are knowngenerically as "fluid catalytic cracking" (FCC).

Relatively, lighter molecular weight and lower boiling pointhydrocarbons, such as gas oils, are typically preferred feedstocks forFCC operations. Such hydrocarbons generally contain fewer contaminantsand have a lower tendency to produce coke during the cracking operationthan heavier hydrocarbons. However, the relatively low content of suchlight hydrocarbons in many current crude mixes has lead to theattractiveness of heavier hydrocarbons, for example residual oils, asfeedstocks to the FCC operation. One problem with the heavierhydrocarbons, however, is that these materials generally contain ahigher level of metals which tend to contaminate the catalyst andincrease the yield of coke during the cracking operation. In addition,the heavier hydrocarbons also tend to contain a greater abundance ofcoke precursors such as asphaltenes and polynuclear aromatics whichresult in increased coke lay.

Several attempts have been made to minimize the negative impact thatheavy hydrocarbon feedstocks tend to have on FCC operation. For example,U.S. Pat. No. 4,552,645-Gartside et al eliminates the problem byavoiding the FCC unit altogether, instead routing the heavy hydrocarbonto a stripper/coker wherein such material is thermally cracked at hightemperatures. U.S. Pat. No. 4,422,925-Williams et al is directed to anFCC process having a plurality of hydrocarbon feedstocks introduced atdiverse locations in a riser type reactor in the presence of a zeolitecatalyst. The lowest molecular weight feedstock is introduced in thebottom of the reactor. Hydrocarbon feedstocks having the highesttendency to form coke are introduced i the uppermost section of theriser and are exposed to the lowest reaction temperature and the lowestcatalyst to oil ratios.

U.S. Pat. No. 4,218,306-Gross et al is assigned to the assignee of thepresent invention and is incorporated herein by reference. Thedisclosure of Gross is consistent with the Williams teaching insofar asit requires converting relatively low coke producing gas oils in a lowerinitial portion of a riser and then a higher coke producing feedstock,such a recycle oil, is introduced in an upper section of the riser.

In typical FCC configurations the feedstocks to be cracked wereintroduced either all together at the bottom of the riser or with theheavier fractions being introduced into the upper portions thereof. Indirect contrast to the state of the art as presented by the abovedescribed patents, applicants have discovered that it is beneficial anddesirable that the heavier, higher molecular weight hydrocarbonfeedstocks, i.e., those feedstocks generally having a relatively hightendency to produce coke, be introduced into the riser at a locationwhich is relatively upstream of the location at which the lighter, lowermolecular weight feedstocks are introduced.

The methods of the present invention may also be used to optimize theslate of reaction products resulting from a single individual feedstock,independently of whether that feedstock is cracked alone or jointly withother individual feedstocks. For example, in certain refinery operatingmodes only a single unblended hydrocarbon stream may be available as FCCfeedstock. According to one embodiment of the present invention, such afeedstock is first separated into light and heavy fractions. Theseparate fractions are then introduced into the reactor such that theheavy fraction enters the riser at a point relatively upstream of thelight fraction. In this way, the conditions under which the light andheavy fractions are cracked may be optimally adjusted according to theteachings of the present invention.

According to certain preferred embodiments of the present invention, arelatively heavy hydrocarbon feedstock, such as residual oil, is used asa fresh feed to an FCC cracking unit for initially contacting suspended,hot and relatively active regenerated catalyst at an elevatedtemperature in a disperse phase catalytic conversion zone. Thereafter, alighter hydrocarbon feedstock, such as gas oil, is injected into adownstream portion of the disperse phase suspension. Thus the relativelyheavy hydrocarbon feedstock will be in contact with the catalyst foronly a portion of the residence time available in the riser beforecoming in contact with a lighter hydrocarbon feedstock. Although it iscontemplated that the heavy hydrocarbon may be introduced at anylocation within the riser provided its relative position to the lighterfeedstock is maintained, according to certain preferred embodiments therelatively heavy hydrocarbon is introduced into the bottom of the riserwhere it is contacted with catalyst. The catalyst introduced into thebottom of the riser generally comprises freshly regenerated catalystwhich enters the riser at an elevated temperature relative to thehydrocarbon feedstocks. The catalyst temperature entering the riser isgenerally greater than about 1100° F., preferably between about 1200°and 1450° F., while the temperature of the hydrocarbon feedstock isconsiderably less, generally less than about 800° F., preferably betweenabout 300° and 600° F. Applicant has found that segregation of thefeedstocks as taught by the present invention produces heavy hydrocarbonreaction temperatures which may be readily optimized according to theparticular feedstock mix to be cracked. As the term is used herein,heavy hydrocarbon reaction temperature refers to the mix temperature inthe heavy hydrocarbon reaction zone of the riser. As the term is usedherein, heavy hydrocarbon reaction zone refers to the portion of theriser between the heavy hydrocarbon injection location and the lighthydrocarbon injection location. As will be appreciated by those skilledin the art, the intimate contact between the heavy hydrocarbon and thehot catalyst which occurs at the entrance to the heavy hydrocarbonreaction zone will result in an initial heavy hydrocarbon/catalyst mixtemperature which is between the temperature of the heavy hydrocarbonand the hot catalyst, depending upon the catalyst to oil ratio. For thepurpose of convenience, the initial mix temperature in the heavyhydrocarbon reaction zone is herein defined as the initial adiabatictemperature of the mixture. This temperature is readily calculated byperforming an enthalpy balance around the entrance to the heavyhydrocarbon reaction zone and by assuming no heat of reaction at theentrance. As is also understood by those skilled in the art, thetemperature in the heavy hydrocarbon reaction zone generally decreasesas the suspension passes upwardly through the zone and the endothermicreaction proceeds. Thus the temperature profile of thehydrocarbon/catalyst mix generally decreases continuously along thelength of the heavy hydrocarbon reaction zone. The extent of thetemperature decrease is a function of many parameters, includingfeedstock and catalyst characteristics and reaction zone configuration.The effect of these parameters and hence the mix temperature at the exitof the heavy hydrocarbon reaction zone can generally be estimated bythose skilled in the art for any particular set of conditions. At theinterface of the heavy hydrocarbon reaction zone and the lighthydrocarbon reaction zone there will be a relatively discontinuoustemperature drop due to the quenching effect of the light hydrocarbonfeedstock. For the purpose of convenience, the initial mix temperaturein the light hydrocarbon reaction zone is herein defined as the initialadiabatic temperature at the light hydrocarbon injection location. Thistemperature is readily calculated by performing an enthalpy balancearound the entrance to the light hydrocarbon reaction zone and byassuming no heat of reaction at the entrance.

The methods of the present invention thus allow the heavier hydrocarbonsto be initially cracked at temperatures which are higher than wouldotherwise be possible in a typical FCC process. Since only a portion,preferably a minor portion, of the total hydrocarbon charged to theriser is initially contacted with the hot, freshly regenerated catalyst,the temperature of the initial catalyst/hydrocarbon suspension is higherthan the temperature which would result if both the heavy hydrocarbonand light hydrocarbon feedstocks were introduced together at a singlelocation in the riser. Accordingly, one important aspect of the presentinvention resides in "blasting" the heavy hydrocarbon feedstock tocatalyst mix temperatures which are higher than otherwise attainablewithout simultaneously subjecting the light feedstock or fractions tosuch unusually high temperatures. High temperature cracking ofrelatively heavy hydrocarbon feedstock increases the production of thepreferred products at the expense of undesirable coke, without exposingthe light hydrocarbons to such temperatures. Initial mix temperature inthe heavy hydrocarbon reaction zone are preferably from about 1050° toabout 1250° F., and more preferably from about 1100° F. to about 1200°F.

According to a further step of the present invention, a lighterhydrocarbon feedstock is introduced into the riser at a location whichis downstream with respect to the heavy hydrocarbon feed injectionlocation. The injection point for the light hydrocarbon feed ispreferably selected to ensure that the contact time in the heavyhydrocarbon reaction zone or the blast zone of the riser is shortrelative to the contact time available in the entire riser. In this way,introduction of the lighter hydrocarbon feed into the suspension acts asa quench for the heavy hydrocarbon reaction and prevents overcrackingwhich would otherwise occur at the relatively high temperatures existingin the heavy hydrocarbon reaction zone. Although applicant does notintend to be bound by or to any particular theory, applicant believesthat processes according to the present invention result in vaporizationand primary cracking of the asphaltenes, polynuclear aromatics, andother high molecular weight components of the heavy hydrocarbonfeedstock at relatively high temperatures which promote the formation ofdesirable products at the expense of coke. Moreover, the period ofcontact at such relatively elevated temperatures, i.e., the contact timein the heavy hydrocarbon reaction zone, is made relatively short by thedownstream introduction of the lighter hydrocarbon feedstocks which tendto quench the reaction and thereby reduce the reaction temperatures. Inthis way, undesirable secondary cracking of the reaction productsproduced in the heavy hydrocarbon reaction zone is minimized.

Accordingly, one important aspect of the present invention resides inreducing the temperature of the hydrocarbon/catalyst suspension at theexit of the heavy hydrocarbon reaction zone. Thus, injection of lighthydrocarbon feedstock into the riser produces an initial lighthydrocarbon reaction zoned temperature which is relatively low comparedto the reaction temperature at the exit of the heavy hydrocarbonreaction zone. As the term is used herein , light hydrocarbon reactionzone temperature refers to the temperature in the light hydrocarbonreaction zone of the riser. For the purposes of convenience, the portionof the riser reactor down stream of the introduction of the lighthydrocarbon feedstock is referred to as the "light hydrocarbon reactionzone", although this term is in no way limiting with respect to the typeof hydrocarbon feedstocks which may be additionally introduced into theriser downstream of the light hydrocarbon feedstock injection location.At the interface of the heavy hydrocarbon reaction zone and the lighthydrocarbon reaction zone there will be a relatively discontinuoustemperature drop due to the quenching effect of the light hydrocarbonfeedstock. For the purpose of convenience, the initial mix temperaturein the light hydrocarbon reaction zone in herein defined as the initialadiabatic temperature at the light hydrocarbon injecting location. Thistemperature is readily calculated by performing a enthalpy balancearound the entrance to the light hydrocarbon reaction zone and byassuming no heat of reaction at the entrance. Once again, the presentinvention is not limited to any particular temperature range in thelight hydrocarbon reaction zone since this temperature will also beeffected by many conditions, including but not limited to feedstockproperties, desired FCC product rate and catalyst circulation rate.Nevertheless, applicant has found that the initial mix temperature inthe light hydrocarbon reaction zone is preferably from about 950° toabout 1050° F., and more preferably from about 980° to about 1020° F. Interms of quenching capacity, applicant has found that the introductionof the light hydrocarbon into the suspension is preferably sufficient toassure a reduction in suspension temperature of at least about 50° F.,and more preferably at least about 100° F., with even better resultsachieved with even more quenching, e.g., there are benefits to operatingwith 150° to 250° F. of quench.

According to a further step required by some embodiments of the presentinvention, the hydrocarbon/catalyst suspension, after the introductionof the light hydrocarbon feedstock, is further passed through the riserreactor for a contact time which is relatively long compared to thecontact time in the heavy hydrocarbon reaction zone. According tocertain preferred embodiments, the contact time in the heavy hydrocarbonreaction zone is preferably less than about half the contact time in thelight hydrocarbon reaction zone, and more preferably less than aboutone-third the contact time in the light hydrocarbon reaction zone.According to certain embodiments, the contact time in the heavyhydrocarbon reaction zone is preferably less than about one-fifth thecontact time in the light hydrocarbon reaction zone.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a catalytic cracking process wherein aheavy feed comprising non-distillable hydrocarbons is catalyticallycracked in a riser reaction zone by contact with a source of hot,regenerated cracking catalyst to produce catalytically cracked productsand spent cracking catalyst, cracked products are withdrawn as products,and spent cracking catalyst is regenerated in a catalyst regenerationmeans to produce hot regenerated cracking catalyst which is recycled tcontact said heavy feed, characterized by: blasting in a blast zone inthe base of the riser a heavy feed containing at least 10 wt %non-distillable hydrocarbons by contacting same with hot regeneratedcracking catalyst at a cat:feed weight ratio of a least 5:1 and whereinthe amount and temperature of the hot regenerated catalyst aresufficient to produce a catalyst/heavy feed mix temperature of at least1050 F., and thereby inducing both thermal and catalytic reactions insaid heavy feed; and quenching in a quench zone within said riserreactor within 2 seconds said mixture with a reactive quench materialwhich undergoes endothermic reactions at the conditions present withinsaid quench zone, and reactive quench is added in an amount at leastequal to 100 wt % of said non-distillable hydrocarbons added to saidblasting zone.

In another embodiment, the present invention provides a catalyticcracking process wherein a heavy feed comprising more than 10 wt %hydrocarbons boiling above 500 C. is catalytically cracked in a riserreaction zone by contact with a source of hot, regenerated crackingcatalyst to produce catalytically cracked products including a viscousheavy fuel oil product and spent cracking catalyst, cracked products arewithdrawn as products, and spent cracking catalyst is regenerated in acatalyst regeneration means to produce hot regenerated cracking catalystwhich is recycled to contact said heavy feed, characterized by: blastingin a blast zone in the base of the riser said heavy feed by contactingit with hot regenerated cracking catalyst at a cat:feed weight ratio ofa least 10:1 and wherein the amount and temperature of the hotregenerated catalyst are sufficient to produce a catalyst/heavy feed mixtemperature of at least 1100 F., and induce both thermal and catalyticreactions in said heavy feed; said thermal reactions being sufficient toreduce the viscosity of said viscous heavy fuel oil product, quenchingin a quench zone within said riser reactor within 1 second said mixturewith a reactive quench material which undergoes endothermic reactions atthe conditions present within said quench zone, said reactive quenchbeing added in an amount equal to 100 to 1000 wt % of saidnon-distillable hydrocarbons added to said blasting zone and sufficientto quench the temperature by at least 150 F.; and recovering from saidcracked products discharged from said riser reactor a heavy fuel oilproduct having a reduced viscosity.

In a more limited embodiment, the present invention provides a catalyticcracking process wherein a heavy feed containing at least 25 wt % residis catalytically cracked in a riser reaction zone by contact with asource of hot, regenerated cracking catalyst to produce catalyticallycracked products including a viscous heavy fuel oil product and spentcracking catalyst, cracked products are withdrawn as products, and spentcracking catalyst is regenerated in a catalyst regeneration means toproduce hot regenerated cracking catalyst which is recycled to contactsaid heavy feed, characterized by: blasting in a blast zone in the baseof the riser said heavy feed by contacting it with hot regeneratedcracking catalyst at a cat:feed weight ratio of a least 15:1 and whereinthe amount and temperature of the hot regenerated catalyst aresufficient to produce a catalyst/heavy feed mix temperature of at least1200 F., and induce both thermal and catalytic reactions in said heavyfeed; said thermal reactions being sufficient to reduce the viscosity ofsaid viscous heavy fuel oil product, quenching in a quench zone withinsaid riser reactor within 0.5 seconds said mixture with a gas oil orvacuum gas oil feed added in an amount equal to at least 200 wt % ofheavy feed and sufficient to quench the temperature by at least 150 F.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Resid Blasting

For maximum effectiveness, it is beneficial if the resid feed, or heavyfeed containing large amounts of resid, is subjected to unusually severeprocessing in the base of the riser reactor.

The unusual severity can be achieved by using conventional cat:oilratios, but somewhat hotter catalyst, a severe preheating step, whichpreferably borders on visbreaking, or by contact with large amounts ofcatalyst. In most units, the preferred method of achieving blastconditions will be to operate with cat:oil ratios which are at leasttwice as high as those used for conventional cracking. While cat:oilratios vary greatly from refinery to refiner, and vary greatly in thesame unit in response to changes in unit operation, catalyst activity,or demand for products, those skilled in the art will be readily able ina given unit to double the cat to oil ratio over what had beenconventionally used at that refinery for cracking of conventional feeds,e.g., gas oils, vacuum gas oils, or gas oils containing minor amounts ofresid.

In most units, resid blasting requires operation with cat:oil ratiosgreater than 5:1, and it will usually be preferred to operate withcat:oil ratios exceeding 10:1 or 15:1, or even higher.

The cat:oil ratio in the blast zone will usually not be the same as thecat:oil ratio exiting the riser. This is because the present inventionwill generally produce a non-constant catalyst/oil ratio profile alongthe length of the riser. That is, the catalyst/oil ratio will decreaseas more hydrocarbon is introduced downstream of the blast zone. Thus theblast zone is generally subject to catalyst/oil ratios which are greaterthan in any other place in the riser. It is possible to achieve blastingwithout resort to unusually high cat:oil ratios, by resort to severepreheating, or hotter catalyst, as discussed hereafter.

Severe preheating will ameliorate to some extent the need for morecatalyst, or hotter catalyst. Thus it is preferred to operate with residrich feed preheat exceeding the amount of preheat conventionally used,typically 300 to perhaps 700 F., i.e., with a feed preheat from 500 to800 F., and even higher if the unit can achieve it. Severe preheatingnot only reduces the viscosity of the heavy feed, but also generates acertain amount of cutter solvent, and reactive fragments which areamenable, for a short time, to catalytic upgrading in the FCC. Expressedas ERT severity (Equivalent Reaction Time at 800 F., in seconds) it ispreferred to operate with a feed which has been given a thermaltreatment equivalent to from 100 to 1000 ERT seconds.

In many units it will also be possible to use hotter catalyst, and moreconventional cat:oil ratios. Because of the large amounts of ConradsonCarbon Residue associated with the heavy feeds contemplated for useherein, the regenerator will probably be pushed to a very hightemperature in trying to burn all the coke produced by cracking a heavyfeed containing a large amount of resid. It is also possible, and willbe preferred in many instances, to use a two stage regenerator, whichcan produce catalyst of extremely high temperature. Such a two stageapproach allows catalyst to be regenerated at extremely high temperatureby performing the regeneration in two stages, the first stage atrelatively moderate temperature, to burn off the fast coke and removemost of the water precursors. The second stage of regeneration can be ata much higher temperature, because it can be a relatively dryregeneration. Thus catalyst need only be thermally stable to retainactivity, not hydrothermally stable.

Quench

It is essential to rapidly quench the heavy feed within no more than asecond or two, or preferably even less, of the blasting stage. Thenature and amount of quench fluid can be selected to reduce temperaturesof resid rapidly and profoundly, preferably to reduce the temperature byat least 100 F., and more preferably by at least 150 F., and mostpreferably by at least 200 F., or more, within a period of no more thana second, preferably 0.5 seconds maximum, and most preferably within 0.2seconds or less.

It is possible, but not preferred, to use conventional quench fluids,such as water, steam, or inert vaporizable liquids, such as cycle oilsand slurry oils, or other aromatic rich streams. Although such quenchfluids will remove heat from the blasted resid, and allow recovery ofthis heat in downstream processing operations, it converts relativelyhigh grade energy into much lower grade heat. The worst scenario, froman energy conservation standpoint, is to convert the energy of blastedresid, at a temperature of around 950-1100F., to low grade condensingsteam in the main column. Use of large amounts of water or steam quenchalso usually results in production of large amounts of sour water, whichcreates a disposal problem. Water also takes up a large portion of thevolume of the FCC plant, and downstream vapor recovery equipment, e.g.,addition of just 5% water to an FCC cracking a conventional feed such asVGO +5 or 10% resid results in about half of the riser reactor volumebeing occupied by steam.

Endothermic Quench

Use of a crackable, or at least reactive, quench liquid, which quenchesthe resid by promoting one or more endothermic reactions, is preferred.We discovered that it is both possible, and beneficial, to use as thequench fluid the conventional feed to a cat cracking unit, e.g, a gasoil or vacuum gas oil. Use of a conventional feed as a quench liquid ispreferred for several reasons. The most significant reason is that mostFCC units must crack a variety of feeds, ranging from resid rich feedsto more conventional stocks such as gas oils and vacuum gas oils andmixtures thereof, hereafter simply referred to as "VGO" for convenience.By using distillable, but crackable, stocks such as VGO as quench,unnecessary blasting and overcracking of VGO in the blasting zone isprevented or at least minimized. The VGO is effective at preventingovercracking of blasted resid, and the VGO is efficiently heated bysuperheated, blasted resid. The VGO, or other distillable, conventionalfeeds are never subjected to thermal cracking in the riser, because thetemperatures experienced by the GO or VGO are similar to thoseexperienced in units which operate without a resid blasting zone. It isirrelevant to the VGO that much of the heat needed to vaporize the VGOcomes by desuperheating overheated resid and the products of blastingthe resid, as opposed to vaporization of resid by removing sensible heatfrom hot, freshly regenerated catalyst.

It is preferred that the quench stream be at least 90% distillable, andpreferably 95% distillable, and most preferably 100% distillable. It isespecially preferred to have a splitter column just upstream of the catcracker, to split the total feed into at least a heavy fraction,preferably containing over 90% of the non-distillable material fed tothe cat cracker, and a lighter fraction, comprising at least 90%distillable hydrocarbons.

Other reactive quench fluids can also be used which will react with theresid, such as alcohols and ethers, and olefinic streams, provided thatsuitable catalysts are also present in a form and an amount which willpromote the desired endothermic reaction. An additive quench fluid, suchas an alcohol, may be used in addition to, or instead of, quenching withVGO and/or water or steam.

Riser Top Temperature

Although conditions at the base of the riser are far more severe thanthose associated with conventional FCC operations, the FCC unit at thetop of the riser, and downstream of the riser, can and preferably doesoperate conventionally. When processing large amounts of resids,especially those which contains large amounts of reactive material whichreadily forms coke in process vessels and transfer lines, it may bepreferable to operate with conventional, or even somewhat lower thannormal riser top temperatures. Riser top temperatures of 950-1050 willbe satisfactory in many instances.

Catalyst Activity

Conventional FCC catalyst, i.e., the sort of equilibrium catalyst thatis present in most FCC units, can be used herein, but will not lead tooptimum results. It is possible, by picking less than optimum conditionsfor blasting, and use of ordinary equilibrium FCC catalyst, to reduceconversion of GO or VGO enough so as to achieve little or no benefitoverall, as far as conversion is concerned. By this is meant that theenhanced conversion of resid due to resid blasting can be largely oreven completely offset by reduced conversion of conventional feed,unless care is taken to optimize the extent and severity of blasting,the amount of quenching, and catalyst activity.

For optimum results, it is important to use the following type ofcatalyst, or at least to add a significant amount of such catalyst tothe unit's inventory.

The preferred catalysts are those which have a relatively high zeolitecontent, which should be in excess of 30 wt % large pore zeolite, andpreferably approaching or even exceeding 50 wt % large pore zeolite. Thelarge pore zeolite preferably has a relatively small crystal size, tominimize diffusion limitations. The zeolites should be contained in amatrix which has a relatively high activity, such as a relatively largealumina content. Especially preferred is use of a high activity matrixcomprising at least 40 wt % alumina, on a zeolite free basis and havingsufficient cracking activity to retain at least a 50 FAI catalystactivity within said quench zone. Ideally, a catalyst is used whichretains at least a 55 FAI cracking activity within said quench zone.

The catalyst will also benefit from the presence of one or more metalpassivating agents in the matrix.

The catalyst should also be formulated to have a relatively large amountof its pore structure as large macropores. Many catalysts having atleast some of these properties have been developed, primarily forcracking resids mixed with conventional feeds. These resid crackingcatalyst are highly preferred for use in the process of the presentinvention, because conventional equilibrium FCC catalysts now widelyused can be overwhelmed by cracking resid rich fractions. Use of acatalyst having the preferred characteristics described above allowssignificant blasting of resid or other heavy feed in the base of theriser, while retaining enough activity to permit vigorous conversion ofthe reactive quench, e.g., VGO, added higher up in the riser.

Thermal Reactions

Even if the catalyst is rapidly deactivated by blasting resid, such thatthere is little or no overall gain in conversion or gasoline yield, theprocess of the present invention is still beneficial because of theimproved properties of the heavy products. By subjecting the resid, or aresid rich fraction, to resid blasting, a significant amount of thermalconversion will occur, which will reduce the viscosity of the heavyproduct. Adding a heavy feed, comprising most or all of thenon-distillables, to the resid blasting zone, allows a significantamount of visbreaking like reactions to be achieved in the base of theriser, while still achieving about the same overall conversion, andproduct properties such as gasoline yields and octane, as that achievedby other approaches, such as that disclosed in U.S. Pat. No. 4,818,372.The heavy fuel oil product of '372 will be more viscous than the heavyfuel oil product of our invention, because we achieve more visbreakingin the base of the riser reactor.

Conventional techniques can be used to calculate or estimate the amountof thermal reaction that occurs in the base of the riser, with somecomplications because of almost complete vaporization and endothermiccatalytic reactions.

In general, it is believed beneficial to achieve thermal conversion ofresid equal to roughly 50 to 1000, and preferably 100 to 700 ERT secondsin the riser blast zone. This will provide enough thermal cracking inthe base of the riser to generate heavy "cutter stock" which willsignificantly reduce the viscosity of the heavy fuel oil product.Because of the difficulty of accurately determining ERT in the blastzone, and the importance of heavy fuel oil viscosity as a productspecification, it may be preferable to adjust the blast zone severity soas to obtain at least a 10%, or 20%, or even higher, reduction in theviscosity of a specified heavy fuel oil fraction.

Additive Catalysts

In many instances it will be beneficial to use one or more additivecatalysts, which may either be incorporated into the conventional FCCcatalyst, added to the circulating inventory in the form of separateparticles of additive, or added in such a way that the additive does notcirculate with the FCC catalyst.

ZSM-5 is a preferred additive, whether used as part of the conventionalFCC catalyst or is the form of a separate additive.

The ZSM-5 can be added as a once thru powder, downstream of blasting.

The ZSM-5 can be added as large, fast settling particles, which have anextended residence time in the riser. High silica additives, such asZSM-5 do not deactivate nearly as quickly as the conventional catalystin the riser, so they make high desirable additives for use in theprocess of the present invention.

Feed Composition

The present invention is applicable for use with all FCC feedstocks. Itis contemplated, however, that the present invention will mostfrequently be used with hydrocarbon feedstocks capable of producingrelatively large proportions of gasoline, gasoline blending components,distillates and distillate blending components. Feedstocks of this typegenerally include liquid hydrocarbon feeds. As used herein, the termliquid hydrocarbon refers to those hydrocarbons which are liquid atstandard conditions. Accordingly, the light and heavy hydrocarbons ofthe present invention are each preferably selected from the groupconsisting of residual gas oils, atmospheric gas oils, vacuum gas oils,coker gas oils, catalytic gas oils, hydrotreated gas oils, naphthas,catalytic naphthas, topped crudes, deasphalted oils, hydrotreated resids(HDT resids), hydrocracked resids, shale oil and mixtures of these. Thelight hydrocarbon feedstock is even more preferably selected from thegroup consisting of atmospheric gas oils, vacuum gas, coker gas oils andmixtures of these. The heavy hydrocarbon feedstocks of the presentinvention are even more preferably selected from the group consisting ofresidual gas oils, topped crudes, deasphalted oils, HDT resids,hydrocracked resids, shale oil, hydrocarbons having an API gravity ofless than about 20°, hydrocarbons having an average molecular weight ofgreater than about 300, hydrocarbon s having an initial boiling point ofgreater than about 700° F., hydrocarbons having a CCR content of greaterthan about 1 wt %, and mixtures of these.

The feeds which will benefit most from the practice of the presentinvention are similar to those described in U.S. Pat. Nos. 4,818,372 and4,427,537, namely those feeds which contain at least 10 wt % materialboiling above about 500 C., and preferably those which contain 20, 25,30% or more of such high boiling material. Especially beneficial resultsare seen when the heavy feed contains 50 wt % or more material boilingabove 500 C. A highly preferred chargestock comprises a mixturecontaining at least 50 wt % resid, diluted or mixed with a minority of alighter, more viscous chargestock, such as a gas oil, a vacuum gas oil,or even a heavy naphtha material.

A mixture of resid, and conventional FCC recycle streams, such as lightcycle oil, heavy cycle oil, or slurry oil, can also be used. In thisinstance, the FCC recycle stream acts primarily as a diluent or cutterstock whose primary purpose is to thin the resid feed, to make it easierto pump and to disperse into the resid blasting zone.

Quench Feed Composition

As previously discussed, use of a crackable, or at least reactive,quench liquid, which quenches the resid by promoting one or moreendothermic reactions, is preferred.

The quench feeds can be divided into three categories:

1. Conventional FCC feeds (or fractions)

2. Unconventional hydrocarbon feeds

3. Reactive non-hydrocarbons.

Conventional FCC feeds, e.g, a gas oil or vacuum gas oil which should beentirely distillable, can beneficially be used as quench. These aremerely the conventional feeds to a cat cracking unit, and by using themas quench they can simultaneously be cracked and used as good quenchfluids. The quench feed can also be split into multiple fractions, i.e.,with the resid being blasted in the base of the riser, quenched within0.5 to 1.0 seconds with vacuum gas oil, and quenched again withinanother 0.5 to 1.0 seconds additional residence time with a gas oilboiling range feed. This splitting of the quench feed by boiling range,and adding the lighter fractions higher up in the riser allows thequench operation to be fine tuned to the resid, the amount of residblasting required, and the overcracking or resid and/or vacuum gas oilquench which is required or can be tolerated.

Unconventional hydrocarbon feeds means those materials which are notconventionally fed to an FCC unit. One of the exceptional quenchmaterials is any highly paraffinic material, such as wax, or slack wax.These materials are not usually considered as suitable feeds forconventional FCC processing, but they are uniquely suited for useherein. These paraffinic feeds are fairly difficult to crack, and arerelatively low coking. The hot catalyst and blasted resid effectivelyvaporizes and cracks this paraffinic material, but the paraffins do notdeactivate the catalyst as much as conventional feeds, such as a vacuumgas oil. The waxy feeds especially make unusual amounts of olefins, andlarge amounts of relatively high octane olefinic gasoline, especiallywhen compared to gasoline yields obtained by cracking more aromaticfeeds such as VGO. Use of a paraffinic quench, perhaps followed byadditional quenching steps with reactive feeds, conventional distillablehydrocarbon feeds, or inerts such as water, leads to effective residblasting and efficient paraffin cracking, and increased yields ofvaluable light products.

Other unconventional hydrocarbon feedstocks which make efficient quenchstreams include other easily crackable or upgradeable hydrocarbonsboiling below the gas oil range. Naphthas, light straight run naphthas,reformer feeds, and normal paraffin rich streams rejected by C5 or C6isomerization units are especially effective quench streams.

Unconventional hydrocarbon quench streams also include the normallygaseous hydrocarbons, such as dry gas or wet gas streams generatedaround the cat cracking unit, or light olefinic streams available fromother sources.

Reactive non-hydrocarbons which can be used as quench fluids includealcohols and ethers, provided that suitable catalysts are also presentin a form and an amount which will promote the desired endothermicreaction. In most instances, the FCC catalyst will be sufficient topromote these reactions. An additive quench fluid, such as an alcohol,may be used in addition to, or instead of, quenching with VGO and/orwater or steam.

Use of a reactive fluid for quenching, wherein some heat removal isaccomplished via an endothermic reaction, will not be quite as prompt assimply dumping a heat sink, such as water in. The slight reduction inquenching speed is not of great concern, especially when only theheaviest fractions of the feed are subjected to blast conditions. Whenrapid quenching is of concern, it is also possible to combineendothermic quench with heat sink quench, i.e., to quench first with VGOor GO, then quench again with water or cool catalyst or some other heatsink, so that severe thermal processing of GO or VGO can be avoided. Thesomewhat slower quenching achieved via an endothermic reaction can alsobe accommodated to some extent by starting the injection of reactivequench liquid (the VGO feed, slack, an alcohol, or a mixture of one ormore) a little sooner than would be done if water or some inert fluidwere being used as the quench liquid.

Blast Feed/Quench Feed Ratios

The reactive quench (whether a conventional, distillable hydrocarbonfeed, an unconventional hydrocarbon feed, or a reactive non-hydrocarbon)should be as large a stream, on a molar or on a weight basis, as theheavy feed added to the resid blasting zone. Preferably the reactivequench is present in an amount equal to 100 to 1000 wt % of thenon-distillable material added to the resid blasting zone, morepreferably 150 to 750 wt %, and most preferably 200 to 600 wt % of thenon-distillable feed to the resid blasting zone.

If the heavy feed to the resid blasting zone comprises 50 wt % resid,and 50 wt % distillable material, then 1 to 10 weights of reactivequench should be used for each weight of resid feed. Expressed as ratiosof quench to heavy feed, where the heavy feed includes both the residand any distillable material mixed in with the resid, the quench toheavy feed weight ratio, for the heavy feed just described, should be0.5 to 5.0, preferably 0.75 to 3.75, and most preferably 1 to 3 weightsof reactive quench per weight of total heavy feed to the base of theriser.

EXAMPLE 1

A pilot scale FCC riser reactor having a constant internal diameter ofabout 0.25 inches and an overall length of about 20 feet was provided. Alight Arab virgin gas oil (LAVGO) having an API gravity of about 24.0,an average molecular weight of about 384 and a wt % CCR of about 0.3 wasintroduced along with an equilibrium commercial FCC catalyst (Filtrol75F) having a micro activity test (MAT) of about 65. At the inlet of thereactor the hydrocarbon partial pressure was about 14 psia. The contacttime in the reactor was about 1.8 seconds at a temperature of about1000° F. The crackability, conversion, coke make and gasoline make ofthe LAVGO at various catalyst/oil ratios were found to be as shown inTable 1. As the term is used herein, volume percent conversion of an FCCfeedstock is defined as follows:

    Conversion=100-(HFO+LFO)

where:

HFO=Vol % Heavy Fuel Oil

LFO=Vol % Light Fuel Oil

As used herein, crackability is defined as follows:

    Crackability=Conversion/(100-conversion) PG,25

                  TABLE 1                                                         ______________________________________                                        Light Arabian Vacuum Gas Oil                                                  Catalyst/Oil        Volume %  Weight %                                                                              Volume                                  (Wt/Wt)  Crackability                                                                             Conversion                                                                              Coke    Gasoline                                ______________________________________                                         7       1.9        66        3.9     54.5                                    10       3.1        76        5.1     61.5                                    ______________________________________                                    

EXAMPLE 2

A light Arab atmospheric resid (LAAR) having an API gravity of about17.9, an average molecular weight of about 515 and a wt % CCR of about6.4 was cracked at catalyst/oil ratios of about 4.2, 5.1 and 8 underconditions otherwise identical to those described in Example 1. Theresults of these runs are indicated in Table 2 below.

                  TABLE 2                                                         ______________________________________                                        Light Arab Atmospheric Resid                                                  Catalyst/Oil        Volume %  Weight %                                                                              Volume                                  (Wt/Wt)  Crackability                                                                             Conversion                                                                              Coke    Gasoline                                ______________________________________                                        4.2      1.2        55        6.8     46                                      5.1      1.7        64        7.5     53.5                                    8        2.4        70        9.1     56                                      ______________________________________                                    

A comparison of Tables 1 and 2 indicates that as a function of catalystto oil ratio the crackability of the heavier resid containing feed,i.e., the LAAR, is slightly higher than that of the gas oil alone. Thecomparison also reveals that the resid containing feed produces muchmore coke than the LAVGO. As in is well understood by those skilled inthe art, heat balanced operation generally requires a reduction incatalyst to oil ratio to compensate for the increased coke make. In heatbalanced operation, therefore, the increase in coke production tends toreduce the crackability of the feedstock and hence inhibit cracking ofall the components in the feed. Accordingly, a comparison of Examples 1and 2 indicates that conversion of the heavy hydrocarbon feedstock wouldbe higher if coke make were reduced. A comparison of Examples 1 and 2also indicates that, under heat balanced FCC operating conditions, thecoke precursors in the LAAR resid containing material contribute to lowyields of gasoline.

EXAMPLE 3

A hydrocarbon feedstock blend consisting essentially of 80 wt % Berylvacuum gas oil (BVGO) and 20 wt % Beryl vacuum resid (BVR) was providedto the riser FCC pilot unit described in Example 1. The feedstock blendhad an API gravity of about 22.2, a molecular weight of about 458 and awt % CCR of about 3.3. The feedstock was contacted in the riser forabout 0.8 seconds with an equilibrium commercial FCC catalyst (DavisonRC25) having a MAT of about 69. The inlet hydrocarbon partial pressurewas maintained at about 20 psia. The results from tests conducted atreaction temperatures of about 1000.F and about 1075.F are summarizedbelow in Tables 3 and 4.

                  TABLE 3                                                         ______________________________________                                        Vacuum Gas Oil/Vacuum Resid Blend at 1000° F.                                                          Volume %                                      Weight %  Volume %    Volume %  Gasoline                                      Conversion                                                                              Coke        Gasoline  Plus Alkylate                                 ______________________________________                                        56.5      4.5         46        64                                            59        4.75        47        67                                            69        5.9         54.5      79                                            69        6.3         55.5      78                                            71        6.4         55        81                                            ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Vacuum Gas Oil/Vacuum Resid Blend at 1075° F.                                                          Volume %                                      Volume %  Weight %    Volume %  Gasoline                                      Conversion                                                                              Coke        Gasoline  Plus Alkylate                                 ______________________________________                                        62        4.4         45        70                                            62.5      4.6         47        70                                            68        4.8         50        79                                            73.5      5.9         53.5      85                                            ______________________________________                                    

An analysis of Tables 3 and 4 indicates that, at approximately the sameconversion level, coke production generally decreases as reactiontemperatures increase. This data also indicates that for approximatelyconstant coke production, gasoline selectivity is not substantiallyreduced when high temperature cracking is utilized. Moreover, this dataalso indicates that the yields of gasoline plus alkylate increase withhigher temperature cracking under heat balanced, i.e., constant cokeyield, FCC conditions. In summary, therefore, Example 3 indicates thatan increase in the cracking temperature of a relatively heavyhydrocarbon FCC feedstocks provides improved gasoline selectivity and areduction in the amount of coke produced.

EXAMPLE 4

A relatively light FCC hydrocarbon feedstock consisting essentially of100% vacuum gas oil is provided. A relatively heavy FCC hydrocarbonfeedstock consisting essentially of 25 vol. % vacuum resid and 75 vol. %vacuum gas oil is also provided. The heavy feedstock and the lightfeedstock, each at approximately 300° F., are introduced together in thebottom of a riser reactor in a heavy feedstock: light feedstock ratio ofabout 4:6 on a volume basis. The feedstocks are contacted with anequilibrium catalyst at a temperature of about 1310° F. Sufficientcatalyst is introduced into the riser to produce a catalyst/oil weightratio of about 7.4 and an initial catalyst/hydrocarbon mix temperatureof about 1060° F. The length of the riser is sufficient to give a totalcontact time of approximately about 2 seconds. The conversion, gasoline,alkylate, 650° F.+ and coke yields expected from such an operation areas follows: 71 vol % conversion; 52 vol % gasoline; 28 vol % alkylate;10 vol % 650° F.+ and 6 wt % coke.

EXAMPLE 5

The heavy and light hydrocarbon feedstocks described in Example 4 areprovided. The heavy hydrocarbon feed, i.e., the feed comprising 25 vol %vacuum resid, is injected at the bottom of the same riser into the samecatalyst circulation stream described in Example 4. The contact betweenthe heavy hydrocarbon feed at 300° F. and the recirculating catalyst at1310° F. produced a initial heavy hydrocarbon mix temperature of about1220° F. and a catalyst/oil ratio of about 18.5. At a second injectionpoint located approximately one-tenth of the total reactor length abovethe bottom injection nozzles, the relatively light hydrocarbon feed isintroduced into the suspension, thereby quenching the reactiontemperature to about 1020° F. Accordingly, the heavy hydrocarbonfeedstock is cracked in the heavy hydrocarbon reaction zone atrelatively elevated temperatures for approximately 0.2 seconds. On theother hand, the light hydrocarbon feed will experience essentiallyconventional cracking for about 1.8 seconds in the light hydrocarbonreaction zone. The expected conversion, and gasoline, alkylate, 650°F.+, and coke yields resulting from this operation are as follows: 72.51vol % conversion; 52 vol % gasoline; 34 vol % alkylate; 9.4 vol % 650°F.+; and 6 wt % coke.

EXAMPLE 6

This example shows the amount of viscosity reduction that can beachieved due to higher mix temperatures in a riser cracking FCC using.The feed was a conventional VGO, having a viscosity of 26 centistokes.the following table shows the viscosity of a given heavy fuel oilproduct, as a function of the mix temperature of catalyst and oil in thebase of a riser FCC unit.

    ______________________________________                                                Tmix  Viscosity                                                       ______________________________________                                                600 C.                                                                              15.7 cs                                                                 770 C.                                                                              13.1 cs                                                                 840 C.                                                                              10.1 cs                                                         ______________________________________                                    

DISCUSSION

It will be recognized by those skilled in the art that the process ofthe present invention calls for an unusual operation of the FCC unit.The heavy feed becomes a minority feed stream, and the quench outweighsthe heavy feed, often by a substantial amount. Such an unusual mode ofoperation is necessary to achieve the desired blasting, and thermalupgrading, of the heavy feed to the base of the riser, withoutovercracking the other feed components. By resorting to such unusualoperating procedures it is possible to make a conventional FCC unitoperate as if it had a visbreaker embedded in the base of the riser,which visbreaker operated selectively on the heavy fuel oil product. AnFCC unit of the present invention can achieve a significant amount ofvisbreaking of heavy feed, with essentially none of the capital oroperating expenses of a visbreaker. No separate visbreaker heater isrequired, there is no fractionator associated with the visbreaker, andno production of relatively low value products, such as the thermallycracked gasoline usually produced by a visbreaker.

Use of conventional FCC feeds as the reactive quench allows these feedsto be cracked efficiently, while quenching the thermal reactionsoccurring in the resid blasting zone. When the preferred high activity,high zeolite content catalysts are used, there is little or no penaltyassociated with first exposing the catalyst to resid, and then usingthis same catalyst to crack, e.g., VGO.

Use of unconventional quench materials, whether hydrocarbon derived(such as slack wax) or non-hydrocarbon (alcohols) allows additionalsophisticated upgrading of these materials, in an efficient manner, in amore or less conventional unit. Slack wax can be efficiently convertedinto gasoline, and thereby upgraded from a low value product to muchmore valuable lighter hydrocarbons.

Use of our preferred process allows any quenched riser FCC process tooperate at maximum effectiveness.

Although the invention has been described in terms of a riser reactor,which are the ones in widespread use commercially, the process alsoworks with equal effectiveness in a downflow reactor.

We claim:
 1. A catalytic cracking process wherein a heavy feedcomprising non-distillable and distillable hydrocarbons is catalyticallycracked in a riser reaction zone by contact with a source of hot,regenerated cracking catalyst to produce catalytically cracked productsand spent cracking catalyst, cracked products are withdrawn as products,and spent cracking catalyst is regenerated in a catalyst regenerationmeans to produce hot regenerated cracking catalyst which is recycled tocontact said heavy feed, characterized by:fractionating said heavy feedinto at least a heavy fraction containing at least 10 wt %non-distillable hydrocarbons and at least one lighter fractioncontaining distillable hydrocarbons; blasting in a blast zone in thebase of the riser said heavy fraction by contacting same with hotregenerated cracking catalyst at a cat:feed weight ratio of a least 5:1and wherein the amount and temperature of the hot regenerated catalystare sufficient to produce a catalyst/heavy fraction mixture having atemperature of at least 1050 F., and thereby inducing both thermal andcatalytic reactions in said heavy fraction; and quenching said mixturein a quench zone within said riser reactor within 2 seconds with said atleast one lighter fraction containing distillable hydrocarbons whichundergoes endothermic reactions at the conditions present within saidquench zone, said reactive quench added in an amount at least equal to100 wt % of said non-distillable hydrocarbons added to said blastingzone.
 2. The process of claim 1 wherein the quench is selected from thegroup of hydrocarbon feeds boiling in the gas oil and vacuum gas oilrange, naphtha boiling range hydrocarbons, and normally gaseoushydrocarbons.
 3. The process of claim 1 wherein said reactive quench isadded in an amount equal to 100 to 1000 wt % of said non-distillablehydrocarbons added to said blasting zone.
 4. The process of claim 1wherein said reactive quench is added in an amount equal to 200 to 750wt % of said non-distillable hydrocarbons added to said blasting zone.5. The process of claim 1 wherein said heavy fraction comprises at least50 wt % material boiling above 500 C.
 6. The process of claim 1 whereinthe quenching zone reduces temperatures at least 100 F. within 0.5seconds.
 7. The process of claim 1 wherein the quenching zone reducestemperatures at least 150 F. within 0.5 seconds.
 8. The process of claim1 wherein the quenching zone reduces temperatures at least 200 F. within0.5 seconds.
 9. The process of claim 1 wherein a non-reactive quenchfluid is added to said quench zone in addition to said reactive quench,and said non-reactive quench fluid is present in an amount equal to 10to 100 wt % of said non-distillable feed added to said blast zone.